Then, look up the BMI and Age on these charts for boys, to see if the the BMI is higher than the 85th percentile or 95th percentile lines, which the CDC defines as Overweight boys and Obese thresholds.

Any values of body mass index between the 5th and 85th percentiles, are considered to be within the Normal range for a male child, not overweight or underweight.

Does this page show the average BMI of a boy?

Yes, but only if you are not lazy.

You need to LOOK on the chart, on the “median” blue line.

Here is a more complete on-line version of the boy’s body mass index for Age chart: